Summary: A Brownian motion has been used to derive stopping boundaries for group sequential trials; however, when we observe dependent increments in the data, the fractional Brownian motion is an alternative to be considered to model such data. We compared expected sample sizes and stopping times for different stopping boundaries based on the power family alpha spending function under various values of the Hurst coefficient. The results showed that the expected sample sizes and stopping times will decrease and power increases when the Hurst coefficient increases. With some Hurst coefficient, the closer the boundaries are to that of O’Brien-Fleming, the higher the expected sample sizes and stopping times are; however, power has a decreasing trend for values starting from \(H = 0.6\) (early analysis), 0.7 (equal space), 0.8 (late analysis). We also illustrate study design changes using results from the BHAT study.